The invention relates to a utilization method of tertiary butyl alcohol coproduced by using a device for producing epoxypropane by using a propene and iso-butane cooxidation method. According to the method, after an acetone containing tertiary butyl alcohol solution by-produced by the device is evaporated, the evaporated solution, air and diluent gas and the like constitute mixed gas according to certain proportion, and after the mixed gas is preheated, the mixed gas is subjected to first-stage oxidation. After the composition and temperature of oxidative products obtained through the first-stage oxidation are adjusted, the oxidative products are subjected to second-stage oxidation. After oxidative products obtained through the second-stage oxidation are absorbed, a crude methacrylic acid aqueous solution capable of being used for refining is obtained. By using the method disclosed by the invention, coproduced tertiary butyl alcohol can be directly used for preparing methacrylic acid without refining and purification.